302 BULLETIN 50, UNITED STATES NATIONAL. MUSEUM. 



even cling to rocks or other vertical surfaces; and their nidification 

 presents nothing that may be deemed pecuhar or even specially 

 characteristic. In their flight and manner of procuring their food, 

 however, they differ strikingly from all other birds, in these respects 

 closely resembHng certain insects, especially the crepuscular hawk- 

 moths (Sphingidie). Their food, consisting mainly of small insects 

 but in part also of the nectar of flowers, is mostly gleaned from 

 blossoms, before which they poise, with wings so rapidly vibrating 

 as to be invisible except as a dim haze or halo partly surrounding 

 the body and producing the humming sound from which these birds 

 derive their vernacular name, the bill thrust inside the flower and 

 the slender, semitubular tongue extended into the depths of the 

 blossom. Some species, instead of feeding from flowers, glean their 

 insect food from the bark of forest trees, following along the branches 

 in suspended flight in the same manner that the others pass from 

 flower to flower. In their feeding from flower to flower. Humming 

 Birds, like bees, butterflies, and moths, perform the same office in 

 the economy of nature as insects by transferring pollen from one 

 bloom to another, and thus assisting in the fertilization of plants. 

 In flying from one point to another, the flight of Humming Birds, 

 while essentially direct, is usually more or less undulating, and so 

 extremely rapid that the eye can scarcely follow. Often this flight 

 is accompanied (at least in the case of males of some species) by a 

 more or less remarkable screeching or grating sound, produced 

 mechanically by some pecuharity of wing-structure. 



Diminutiveness of size and metalHc brilliancy of coloring are the 

 chief external characteristics of Humming Birds, though exceptions 

 to both occur; and in these respects they, as a group, have no 

 rivals. Unfortunately stuffed specimens convey but a faint idea of 

 their splendid coloring, for the perfection of their changeable reful- 

 gence can be fully realized only in the Hving bird, whose every 

 change of position flashes to view a diflcrent hue — emerald green 

 replacing ruby red, sapphire blue succeeding fiery orange, or either 

 becoming opaque velvety black — according to the angle at which 

 the sun's rays touch the feathers, an effect which can only partially 

 be imitated with the stuffed specimen by artificially changing its 

 position with reference to the fight. Many species have a spot of 

 the most luminous or brilfiantly metalfic color (usually green) that 

 it is possible to imagine on the forehead at the base of the bill, this 

 spot being surrounded by the most intense velvety black — evidently 

 to enhance the brilfiancy of the ornament by contrast, just as a 

 jeweler w^ould, for the same purpose, display a diamond or other 

 gem against a background of black velvet. Often there is a spot of 

 briUiant color and one of a contrasting hue just below it, the result 



